Very subjective question, and I suspect there'll be lots of input.

I've been all over Caribbean on 3 cruises and a land based week in St
Thomas which had me visiting St Thomas/St. John, Grand Cayman,
Cozumel, Guadeloupe, St Lucia.  Spent a lovely week in the Florida
Keys.  Most recently I spent 10 days in Maui.

Maui was the best vacation I ever took. I'd recommend Maui in a
heartbeat.  It's gorgeous, the snokelling and diving are solid as
well.  There may be better places for snorkeling per se, but my god
does Maui have the complete package as a vacation destination.  Check
out Wailea and Lahaina, and Kanampali areas for hotels and resorts (in
the that order perhaps), and have a lovely time on a gorgeous island
where you can drive everywhere you like, and not feel like a tourist.
You'll not feel guilty about having enough money to travel there
either. I susepect you'll encounter some discomfort in the other two
destinations depending on where you stay and how much you explore.

Maybe add Grand Cayman and the Florida Keys, perhaps Key Largo area
with 2 days in Key West to your itinerary options.

I know nothing about La Paz.  Cancun I've never been to, but comments
about it being fairly overrun with a lot of overt poverty around and
such has prevented me from considering it.  Feel free to disregard
this advice though as it's second hand.  

Arguably, Cozumel is headed in that direction, but there's no arguing
the beauty of the diving and snorkeling available in Cozumel.  I'd go
there again.  It is a foreign country of course, so be careful about
pickin gaccomodations, you'll wanna cab rather than drive, be careful
what you eat, drink only filtered water, don't dare break the law, and
all that jazz.

If you're American, the list of worries drops significantly going to
Maui, but then again, if international travel adds something to the
experience for ya, go for it.  No better education than travelling...

Whatever you decide, good luck and have fun!  But I think you'd be
hard pressed to find anyone saying negative things about Maui.  It's
not the cheapest vacation destination, but there's no place like it
either.  And the cost to get there for better or worse keeps out some
of the negatives in a vacation destination that the proximity of
a poor population can bring (panhandling, vendors complete hawking for
your business, the uneasy feeling if you discover you're wearing a
piece of jewelry, etc.).

Best Regards,
--
Todd H.  
http://www.toddh.net/

Maui, for sure.  You can buy a book called Snorkeler's Guide to Maui or
something like that and it lists 50 or so spots.  At Black Rock you could
rent a tank and do a shallow dive under your snorkeling girlfriend.  Perhaps
she'll flash you if you ply her with enough mai tais.

La Paz has some nice spots north of town past Pichilingue - La Balandra is
good a for day and there are other recommended spots I've never visited.
While this time of year in the Gulf is still too cold for diving, the water
should be warm enough on the surface to allow pleasant snorkeling.

Cancun has a few "theme park" like settings within a 1-2 hour drive that all
start with Xs, such as Xel-Ha and Xcaret, that all promise good snorkeling.
I've never been to any of them but their brochures have pretty pictures.

<BigHaig@feet.com> pounded away at his keyboard resulting in:

Best snorkelling place I have ever seen is at a resort near Santiago
de Cuba.  When I was there it was a Delta.  It then became a
Superclubs and might still be one.

Other very good places are La Source in Grenada and Anse Chastenet in
St Lucia.  Sunset House in Grand Cayman and La Ceiba in Cozumel are
also quite nice.

Snorkelling is not available at Cancun airport.  I have never been to
Maui or La Paz.

Dan Bracuk
If we don't succeed, we run the risk of failure.

Since the subject is a multiple choice of THREE locations on
snorkeling,
I'll vote Cancun, especially for Warm Water Wimps.  :-)

All the Pacific locations are for Cold water Wimps.  I've been to all
3.

Greg should have said "La Paz sucks" because that was more or less what
he said when advising the cruise ship pods.

If Maui doesn't suck, it's over-rated.

Cancun sucks if you're talking about SCUBA, but for snorkelers, all
you need is 10 feet of water and some fish.  Cancun has that.  :)

That's why my vote is Cancun, given your constraints and triple choice.

-- Bob.

Well I went to Cancun and the snorkeling was pretty bad.  I went to Xpu-Ha
and Isla Mujeres, since they were both advertised a great snorkeling spots.
Not so great in my opinion.

Here are some regular pics of the trip www.bighaig.com/cancun2005